Energy Conversion Mechanisms and the Governing Role of Surrounding Rock Stiffness during Strain Bursts

Excess energy to eject fractured rock is a prerequisite for strain bursts. The energy released is contributed by both the burst rock and the surrounding rock mass. This study establishes a quantitative framework identifying the equivalent boundary stiffness as the intrinsic mechanism governing external energy release. The inverse relationship between the energy released from the surrounding rock mass and its stiffness was first verified using a local burst model in FLAC3D (version 6.00). The simulation reveals that as the equivalent boundary stiffness degrades from 61.04 to 7.77 GN/m, the proportion of energy contributed by the surrounding rock mass surges from 15.90% to 62.18%. To account for inelastic dissipation, the framework was further validated via a rigorous back-analysis of a violent rock burst at the Jinping Underground Laboratory Phase II using the Mohr–Coulomb strain-softening model. The results indicate a critical dual-mechanism: lower stiffness not only increases the magnitude of external energy supply but also amplifies the efficiency of its conversion into kinetic energy. For the specific burst event, the surrounding rock mass contributes approximately 50% of the total released energy, of which about 68% is effectively converted into kinetic energy for ejection. These findings confirm that surrounding rock stiffness fundamentally governs the kinetic energy budget in deep underground strain bursts.